The health of Thailand's 88-year-old King Bhumibol Adulyadej, the world's longest reigning monarch, has "overall not yet stabilised", the palace said in a statement on Wednesday.

It follows a statement on Sunday in which the palace said the king was in an unstable condition after receiving haemodialysis treatment.

"On Oct. 11 his blood pressure lowered and breath quickened," the palace said, adding that his health has "overall not yet stabilised".